The ultimate goal of this research is to understand in some detail the pharmacology of individual retinal synapses and their contribution to retinal function. The immediate aim is to explore the possibility that stimulation with light can be used as a method of isolating the effects of a restricted set of retinal synapses for pharmacological study. Rabbit retinas will be removed from the eye and maintained in vitro in a constantly flowing medium. Ganglion cell activity will be recorded extracellularly using metal microelectrodes, and photic stimulatin will be delivered via the reversed optics of a binocular microscope. By probing the retinal surface with small spots of light or with discs and annuli, it will be possible by conventional criteria to describe center or surround contributions to the final ganglion cell response, or to describe the directional preference of cells sensitive to movement. Pharmacological agents will then be introduced into the incubating medium and their effects on receptive field components measured either by spike counting under fixed conditions of stimulation or by measuring the light intensity required to evoke a fixed level of response. Further attention will be paid to possible pharmacological effects on the dynamic properties of the retinal response. Of particular interest are the source of the "spontaneous" firing of ganglion cells and the nature of the mechanism which limits the response of those cells which respond transiently to maintained light. Related work will explore the possibility that central processing of retinal outputs can be investigated by observing the central structures' response to experimentally introduced alteration of the normal retinal output.